This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
In a multitude of commercial applications, it is common to employ conveyor belts for the purpose of transporting products and materials. Such conveyor belts can serve in applications which have minimal demands, moderate demands, or in applications which are extremely demanding and which require heavy-duty conveyor belts. Conveyor belts can also vary greatly in size and length. For instance, the conveyor belts used in mining applications can be up to about three meters wide and very long, for example, on the order of many kilometers. They can also be up to about 8 centimeters thick, or even thicker. In any case, heavy-duty conveyor belts are widely used for moving minerals, coal, agricultural products, and a wide variety of manufactured products from one point to another. For instance, heavy-duty conveyor belts are often used in typical mining applications to transport minerals below the ground, to above the surface, and ultimately above ground to a desired location for processing and/or ultimately for transportation on rail road cars, trucks, barges, or ships.
Conveyor belts are also widely used in a wide variety of applications which have only moderate or even light demands. For instance, conveyor belts are commonly used in conveying groceries and household items at the check-out lanes of grocery stores and supermarkets. Conveyor belts of this type are frequently used for many hours of every day and can be subjected to user abuse caused by spills and contact with items having sharp edges which can cut the surface of the belt. Accordingly, high demands are frequently put on such belts even though the items being conveyed in such applications are normally light and non-abrasive in character. In applications of this type where consumers are using and seeing the conveyor belt it is also important for the conveyor belt to maintain an aesthetically good appearance throughout its service life.
Pipe conveyors, also referred to as tube conveyors or tubular conveyors, are conveyor belts which are loaded with a material to be conveyed and after being loaded are closed into the conformation of a tube by mechanical means to force the conveyor into a closed tube by overlapping the belt edges. After being closed into the form of a tube the material being conveyed is protected from external elements and is also contained within the tube to in help prevent loss of the material being conveyed. In any case, a plurality of support and guide assemblies for the conveyor are situated along the conveyor path to open and close the conveyor as desired at different points along the path of the conveyor. Each assembly includes a plurality of support and guide rollers, which contact and hold the pipe conveyor belt while in operation.
Pipe belts are predominantly employed where bulk material is conveyed in a relatively confined space through horizontal and vertical curves. By virtue of their special adaptability to various topographical conditions, pipe belt conveyor systems are also used for conveying material over distances longer than 1 kilometer. The advantages offered by pipe belts include protection of the transported material against environmental influences (rain, wind, etc.) and protection of the environment against material dropping from the conveyor belt (ashes from power plants, gypsum, etc.). In some cases pipe belts also protect the material being transported from theft by employees and third parties that may be present in the area through which the material is being conveyed.
Pipe conveyor belts are flexed by opening and closing during every cycle of operation to allow for the material being conveyed to be loaded and unloaded from the belt. This opening and closing action subjects the pipe belt a substantial amount of repeated flex which is encountered even during normal operations. In addition to this, pipe belts are prone to running off course or twisting under certain operating conditions. Belts may twist because of uneven loading, uneven guidance through curves, or otherwise poorly aligned systems. For this reason, support and guide rollers are optimally designed to provide for trouble-free and low maintenance operation as the pipe belt travels through the conveyor system. The rollers are individually aligned depending upon the course that the conveyor system is running. The functionality of the rollers is influenced by varying weather and temperature conditions, wear, and design defects. For example, moisture reduces friction between the rollers and the conveyor belt, which results in guidance that is not optimal. If the pipe conveyor belt is misaligned or twisted, for example as it is running up on an ejecting drum, the conveyor belt can fold or even run off of the drum sideways. During any of these adverse operating conditions the pipe belt can be subjected to even more flexing.
In any case, all conveyor belts are flexed during normal operation and can be flexed to an even greater degree during periods of abnormal operation or when being abused. It is accordingly important for most conveyor belts to exhibit a high degree of flex fatigue and dynamic ozone resistance to provide a long service life and to maintain an aesthetically good appearance and optimal functionality. For instance, the aesthetic appearance of a conveyor belt can be quickly destroyed by surface cracking that results from insufficient flex fatigue resistance and dynamic ozone resistance in the outer cover layer of the belt.
Conveyor belts are typically comprised of a polymeric material which has an adequate combination of strength and flexibility to meet the needs demanded in the particular application where the belt will be used. For instance, conveyor belts are commonly comprised of a cured rubber or multiple layers of various cured rubbers. Such conveyor belts also frequently include one or more layers of reinforcement which provide the belt with additional strength and durability. The reinforcement can be comprised of a polymeric fabric or metal reinforcements, such as steel reinforcements.
Conventional conveyor belts which are used in heavy duty applications are typically comprised of a cured rubber as a top layer (the carry cover layer), a cured rubber as a bottom layer (the pulley cover layer), and a reinforcement layer which is situated between the top layer and the bottom layer. The prominent material used in such conveyor belts generally is a moderately flexible elastomeric or rubber-like material, and the belt is typically reinforced by a plurality of longitudinally extending steel cables or cords which are positioned within the belt and extend along the length thereof.
Surface cracking due to inadequate flex fatigue and dynamic ozone resistance is a problem that continues to persist in virtually all types of conveyor belts. It is a particularly difficult problem in pipe belts due to the degree of flexing which they encounter during normal use and which can be aggravated during abnormal operation. Even though surface cracking in the cover layer of many types of conveyor belts is a long standing problem, a means to eliminate it has proven to be elusive. There has accordingly been a long felt need for conveyor belts having better flex fatigue and dynamic ozone resistance in their cover layer to provide longer service life without encountering surface cracking.